![]() The stacking of different oxides disturbs the subtle equilibrium among various interactions, leading to a wealth of exotic quantum states, such as two-dimensional electron or hole gas at the interface of two insulating materials such as LaAlO 3/SrTiO 3 (LAO/STO) 3, 4, the spontaneous magnetic reversal in La 2/3Sr 1/3MnO 3 films 5, a ferromagnetic (FM) interface between nonmagnetic constituents 6, 7, polar magnetic metal phase in BaTiO 3/SrRuO 3/BaTiO 3 heterostructures 8, chiral ferromagnetism in SrRuO 3 films 9, and strain-induced superconductivity in RuO 2 films 10. It also provides a practical approach to engineer material systems via highly localized modifications in their structure and composition that may offer new routes to the design of oxide electronics.Ĭomplex-oxide heterostructures have been established as an effective engineering platform offering prospects to create tunable electro-magnetic functionalities, enabled by manipulation of the cooperative interplay between electronic spin, charge, orbital, and lattice degrees of freedom 1, 2. The results highlight delicate nature of magnetic instability in CaRuO 3 and subtle effects that can alter it, especially the role of A-site cation in electronic and magnetic structure additional to lattice distortion in ruthenates. Atomically resolved imaging and density-functional-theory calculations reveal that the whole δ-doped film preserves the bulk-CaRuO 3 orthorhombic structure, while appreciable structural and electronic changes are highly localized near the SrO layer. However, δ-doping to middle of such CaRuO 3 films induces an insulator-to-metal transition and unusual ferromagnetism with strong magnetoresistive behavior. While bulk CaRuO 3 is metallic and nonmagnetic, films thinner than or equal to ~15-unit cells (u.c.) are insulating though still nonmagnetic. Here we report the emergence of unusual, thickness-dependent properties in ultrathin CaRuO 3 films by insertion of a single isovalent SrO layer (referred to as δ-doping). Heterostructures of complex transition metal oxides are known to induce extraordinary emergent quantum states that arise from broken symmetry and other discontinuities at interfaces.
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